Phosphors



April 4, 1961 s. LARAcH 2,978,417

PHosPHoRs Filed April 25, 1958 4 Sheets-Sheet 1 #wmf/V67# 19 Y .iii/zonZamdz BY /Qm April 4, 1961 s. LARACH 2,978,417

PHosPHoRs 1%? -M Il? f2 IN V EN TOR. .S/Mm/ Ai/10V April 4, 1961 s.LARACH 2,978,417

PHOSPHORS Filed April 25, 1958 4 Sheets-Sheet 4 6000 wmf/WMA Z// @5' jj'INVENTOR.

S/Mo/ LARAcf/ 'United States Parent O PHOSPHORS Simon Larach, Princeton,NJ., 'assigner to Radio Corporation of America, a corporation ofDelaware Filed Apr. 25, I1958, Ser. No. 761,589

9 Claims. (Cl. 252-3015) in general, the mixed chalcogenide phosphors ofthe invention consist essentially of a single phase solid solutions ofsulfo-tellurides, seleno-tellurides, and sulfo- Selene-tellurides ofzinc, cadmium and zinc-cadrnium. A feature of the invention is thediscovery of limited ranges of compositions in thesulfo-seleno-telluride system which produce single phase solidsolutions, which solid solutions produce useful host crystals. Where thehost crystal is principally a seleno-telluride, the host crystal maycontain up to about mol percent of sulfide. Where the host crystal isprincipally a seleno-sulide, the host vcrystal may f contain up to about15 mol percent of telluride. Where the host crystal is principally aselenide, the host crystal may contain up to 33 mol percent of tellurideand/or sulfide. lneicient phosphors result where more than one phase ispresent. Cadmium may replace part or all of f the zinc. The host crystalmay have incorporated therein activator proportions of one or moreimpurities of the group consistingof copper, silver, gold, andmanganese, or may contain no added impurity. Suitable activatorproportions are 0.0001 to 0.5 weight percent with respect to the Weightof said host crystal. Increasing substitutions of tellurium for sulfurand/ or selenium in the host crystal shifts the luminescence emission ofthe phosphor toward the red end of the spectrum. This eiect isnoticeable when as little as` 0.001 mol percent of tellurium is present.The phosphors herein will 'luminesce when excited with electric iields(electroluminescence), cathode rays (cathodoluminescence), or ultraviolet or X-rays (photoluminescence) The preferred cathodoluminescentphosphors herein comprise -a host crystal composed of zincseleno-tellurides rand sulfo-seleno-tellurides containing activatorproportions of one impurity of the group consistingof copper ,andsilver.

The preferred electroluminescent phosphors herein comprise a hostcrystal consisting essentially of zinc seleno-tellurides and zincsulfo-tellurides containing acti- `vator proportions of copper andactivatorV proportions of a member of the group consisting of (1)bromine and (2) bromine and gallium incorporated in said host crystal.

The foregoing objects and other advantages are described in detail byreference to the accompanying drawings in which:

Figure 1 is a family of curves illustrating the spectral distribution ofthe emission from several phosphors of the invention prepared without anactivator and VWithc'n'rt a ux and excited with cathode rays; f'

Figure 2 is a family of curves illustrating lthe spectral distributionof the emission from several phosphorsr of the invention preparedwithout an activator and with r.2

v'silver activator and 2 percent by weight of sodium chloride liux andexcited with cathode rays;

Figure 4 is a family of curves illustrating the spectral distribution ofthe emission from several phosphors-of the invention prepared with 0.01percent by weight of copper activator and 2 percent by weight of sodiumchloride Yilux andexcited with cathode rays;

Figure 5 is a family of curves illustrating the spectral distribution ofthe emission from several phosphors ofthe invention prepared with 0.01percent by Weight of copper activator and 2 percent by weight of sodiumchloride flux and excited with ultraviolet rays; y

Figure 6 is a partially-sectional view of a cathode ray tube having yaluminescent screen on the face plate thereof including a phosphor of theinvention; and

Figure 7 is a partially-sectional, partially-schematic view of anelectroluminescent device including a phosphor of the invention. f v

Figure 8 lis a family of curves illustrating the spectral distributionof the emission from several vphosphors of the invention when excitedwith cathode rays;

Figure 9 is a family of curves illustrating the relative emissionintensity of 0.95 ZnSe': 0.05 ZnTe :Cu (0.01.) crystallized at varioustemperatures as a function yof -current density duringzcathode `rayexcitatiomand Figure l0 is a family of curves illustrating .the spectraldistribution of electroluminescence emission of a phosphor of theinvention compared with a similar phosphor Without tellurium, and

`Figure .11 is a portion of zinc sulfide-zinc selcnide-zinc telluridesystem showing the locationvof the single phase phosphors of the invenftion. I The phosphors in accordance with the invention consistessentially of a single phase solid solution having a composition Withinthe shaded area of FigureV 11. Y -Part :or all of the zinc may bereplaced with cadmium. `The phosphors herein may contain an added,impurity such copper, silver, gold or manganese to enhance thelumines-- cence characteristics thereof, or may contain no added im?purity. Y

The phosphors herein may be approximately described as sulfo-tellurides,sulfo-seleno-tellur-idesV and selenotellurides of zinc and/or cadmium;or. by the molar formula: e

aMlS; bM2Se 0M3Te MHZ) f wherein: M1, M2 and Ma are Veach at least oneYmember of the group consisting of lzinc yand cadmium, M4 is at leastone impurity of Ithe group consisting .of copper, silver, gold andmanganese, and

a=o.0oo to 0.999 when c is 0.15 or less .and l0.000` to' Example1.Slurry a mixture of 94.2 grams of zinc .Patented Apr.` 4, y196.1 1-

a triaxial diagram of the e sulfide and 5.8 grams of zinc telluride intriple-distilled water. Dry and tire the mixture at 900'o C. in anitrogen atmosphere for about 30 minutes. The composition of the tiredproduct calculated from the initial mixture is 0.96 ZnS: 0.04 ZnTe.Referring to Figure 1, the spectral distribution of the emission fromthis phosphor when excited with cathode rays is shown by the curve 23.Other phosphors prepared without an activator and without a flux areshown in Figure 1. AIncreasing proportions of ZnTe up to `about 8 molepercent shifts APKCR (the peak wavelength under cathode ray excitation)toward the red end of the spectrum PKCR remains substantially constantwith further increases in ZnTe.

Example 2.Slurry a mixture of 89.0 grams of zinc sulfide,4 11.0 grams ofzinc telluride and 2.0 grams of sodium chloride in triple-distilledwater. Dry and fire the mixture at 1000 C. in a nitrogen atmosphere forabout 30 minutes. The composition ofv the fired product calculated fromthe initial mixture is 0.94 ZnS:0.06 ZnTe. Referring to Figure 2, thespectral distribution of the emission from this phosphor when excitedwith cathode rays is shown by the curve 34. Other phosphors preparedwithout an activator but with a sodium chloride flux are shown in Figure2.

The inclusion of NaCl during synthesis has several eiects: l) the unuxedphosphors with up to 2 mole percent ZnTe have XPKCR (peak wavelengthunder cathode ray excitation) at about 465 A; (2) with incorporation ofZnTe up to 2 mole percent in the fluxed phosphors, there is a decreasein PKCR to 5190 A. for 0.90 ZnS:0.10 ZnTe; (3) the iiuxed materials donot show a levellingoff of XPKCR at 8 percent ZnTe, as do unfluxedphosphors; (4) fluxed materials with 6 to 10 mole percent ZnTe show asecondary emission band, with APK at about 6000 A. The peak emissionintensities decrease with increasing proportion of ZnTe, thelevelling-off point occurring at about 8 mole percent ZnTe.

Example 3.-To a mixture of 95 grams of zinc sulfide and 5.0 grams ofzinc telluride, add 0.0'1 gram of silver, as an aqueous solution ofsilver nitrate, and 2 grams of sodium chloride. Slurry the mixture withtriple-distilled water, dry and re at 900 C. in a nitrogen atmospherefor about 45 minutes. The composition of the tired product calculatedfrom the composition of the initial mixture is 0.98 ZnS:0.02 ZnTezAg(0.01). Referring to Figure 3, the spectral distribution of the emissionfrom this phosphor when excited with cathode rays is shown by the curve41. Other phosphors prepared with silver as the activator and sodiumchloride as the iiux are shown in Figure 3.

The addition of a silver activator has the following effects: (l)increasing additions of Ag, shifts PKCR toward shorter wavelengths; (2)with proportions of ZnTe greater than about 4 mole percent, PKCR shiftstoward the longer wavelengths, with an indication that levellingoff isoccurring at about 10 mole percent of ZnTe; (3) the secondary (6000 A.)band, present in phosphors without Ag, is absent in the correspondingphosphors containing Ag; (4) the decrease of 69K (peak'emissionintensity) for materials with Ag is very similar to that of materialswithout Ag prepared Vwith NaCl tiux.

Example 4.--To a mixture of 89 grams of zinc sulfide and 1l grams ofzinc telluride, add 0.01 gram of copper, as an aqueous solution ofcopper chloride, and 2 grams of sodium chloride. Slurry the mixture withtriple-distilled water, dry and then fire the mixture at 900 C. in anitrogen atmosphere for about 30 minutes.

The composition of the red product calculated from the composition ofthe initial mixture is 0.94 ZnS:0.06 ZnTe: Cu (0.01). Referring toFigure 4, the spectral distribution of the emission from this phosphorwhen excited with cathode rays is shown by the curve 53. Referring toFigure 5, the spectral distribution of the emission from this phosphorwhen excited with ultra- 4 violet is shown by the curve 62. Otherphosphors prepared with copper as the activator and sodium chloride asthe liux are shown in Figures 4 and 5.

The addition of a copper activator has the following effects on spectraldistribution as a function of ZnTe proportion: (1) With ZnTe proportionsup to about l0 mole percent, the spectral distribution consists of atleast two bands, (a) a blue (4600 A.) band of Zn(S:Te), NaCl, and (b) agreen band of copper. `Under UV excitation, the blue band is notevident, and the peak wavelength is shifted toward longer wavelengthsmore rapidly, than with CR excitation.

Example 5.-To a mixture of 94.2 grams of zinc sulde and 5.8 grams ofzincv telluride, add 0.5 gram of manganese, as manganese chloride, and2.0 grams of sodium chloride. Slurry the mixture with triple-distilledwater, dry and then re the mixture at about 1000 C. in a nitrogenatmosphere. The composition of the iired product calculated from thecomposition of the initial mixture is 0.96 ZnS:0.04 ZnTe:Mn (0.5). Thisphosphor exhibits a peak emission wavelength at 4620 A. when excitedwith cathode rays.

The phosphors prepared with 'Mn activator exhibit two emission bands,designated as Band I Whose peak wavelength was at 4800 A. and Band Ilwith peak wavelength at 5950 A.

Referring to Table I, increasing ZnTe shifts the MKG of Band I, forphosphors prepared with NaCl and without NaCl, toward the red end of thespectrum. Increasing proportions of manganese shifts Band I toward theblue end of the spectrum.

Table l EFFECT oF MANGANESE oN PEAK WAVELENGTH or BAND I EMISSION FROMZn(S:Te) PHOSPHORS Peak Wavelength N aCl Without NaCl Host CrystalUnactl- Unuctivated, Mn, A. vnted, Mn, A

The sulfo-tellurides are described with respect to particular zincsulfo-tellurides. Cadmium may be substituted for part or all of the zincin the phosphors herein. The substitution of cadmium for zinc shifts thepeak spectral emission of the phosphors of the invention toward the redend of the spectrum. The ratio of zinc plus cadmium to sulfur plustellurium is about 1 to l.

Sulfur, tellurium, zinc and cadmium may be introduced in elemental formor as compounds which are decomposed 4upon heating to yield the elementsinto the reaction. It is preferred to introduce these elements assuliides and tellurides of zinc and cadmium. The sulde and telluridestarting materials should be of luminescencegrade-purity, and shouldcontain no spectrographicallydetectable impurities. The synthesis ofpure zinc sulfide and cadmium sulfide is described by H. W. Leverenz inIntroduction to Luminescence of Solids, Wiley (1950), New York. Zinctelluride may be obtained by adding elemental tellurium, in severalsmall portions, to molten zinc, at about 800 C., in an atmosphere ofhydrogen. The temperature is then raised to l300 C., and held for 15minutes, to boil off unreacted zinc and tellurium. After cooling, thezinc telluride is ground and siftcd through a mesh screen.

Zinc telluride is soluble in zinc sulfide to the extent of 1about 10mole percent, when no selenium is present. Similarly, zinc sulfide issoluble in zinc telluride to the '5 extent of about mole percent. Ihis'is unexpected because of the difference in the ionic radius of sulfur(ionic radius=1.84 A.) and tellurium (ionic radius :2.21 A.). Hence, twophases are present in the range 90 mole percent zinc sulfide 10 molepercent zinc telluride to 5 mole percent zinc sulde: 95 mole percentzinc telluride. lOnly a single phase is present beyond this range. Theinvention contemplates single phase sulfotellurides of zinc, cadmium andzinc-cadmium with or without an activator and prepared with or without aflux.

Any of a number of activators may be used, alone or in combination. Forexample, one may use silver, copper, gold or manganese or combinationsthereof. The optimum amount of copper, silver and gold activator isapproximately 0.01 percent by weight with respect to the weight of thehost crystal; i.e., the combined weight of zinc, cadmum,`selenium andtellurium. The proportion of copper, silver andqrgold: activator may bevaried in between 0.0001 and 0:1 percent by weight with respect to theweight ofthe host crystal. Copper, silver and gold preferablyv areintroduced as salts, such as chlorides or nitrates. Manganese may beused as the activator in the range between 01.01 and 2.0 percent byweight, preferably 1.0 percent by weight..

A halide flux may `be added to assist the recrystallization of the hostcrystal. Chlorides, bromides and iodides of alkali metals, alkalineearth metals and volatile cations may be used. For example, sodiumchloride, ammonium chloride, calcium bromide and sodium iodide may beused. Sodium chloride is the preferred flux. Between 0.1l toV 10.0percent byweight of flux with respect to the weight of host crystal maybe used. The preferred proportion is 2.0%. A non-oxidizing atmosphere,such as argon, nitrogen or hydrogen, preferably nitrogen, may be used.The Vfiring may be carried out within the range between 700 C. and 1300"C., however, a iiring temperature of 900 C. is preferred. Firing shouldbe carried on until the solid state reactions take place. The durationof tiring depends in part on the batch size. It is preferred to iire'thebatches of the examples for about 30 to 45 minutes.

II. SELENO-TELLURIDES Example 6.-To a mixture of 93.5 grams of zincselenide and 6.5 grams of zinc telluride, add 0.01 Igram of copper as anaqueous solution of copper chloride and 2 grams of ammonium chloride.Slurry the mixture with triple distilled water, dry and then tire themixture at 900 C. in a nitrogen atmosphere for about 30 mintites.

The composition of the fired product calculated from the composition ofthe initial mixture is 0.95 ZnSe:0.05 ZnTe:Cu (0.01). Referring toFigure 8, the spectral distribution of the emission from thisphosphorwhen excited with cathode ray excitation Vis shown Iby curve 24.Referring to Figure 9, the relative peak emission intensity of thisphosphor as a function of current density is shown by curve 38.

Example 7.-To a mixture ofy 97.0 4grams of zinc selenide and 3.0 gramsof ZnTe, add 0.01 gram of copper as an aqueous solution of coppernitrate and 2 grams of ammonium chloride. Slurry the mixture with tripledistilled water, dry and iire at 900 C. in a nitrogen atmosphere forabout 45 minutes. The composition of the tired product calculated fromthe composition o-f the initial mixture is 0.98 ZnSe:0.02 ZnTe:Cu(0.01).

The selenotelluride phosphors are described with respect to particularzinc seleno-tellurides. Cadmium may ybe substituted for part or all ofthe Zinc in the composition of the invention. The substitution ofcadmium for zinc shifts the peak spectral emission toward the infraredend of the spectrum. Zinc telluride and Zinc selenide 4for single phasesolid solutions in all proportions when no sulfur is present. Someof thephosphors of the invention are therefore referred to asseleno-tellr'ides. The effect ofsubstituting tellurium' for *seleni umis to shift the peak spectral emission of' the phos``r` phors of theinventionrtoward thev infrared end ofthe spectrum. The ratio of zincplus cadmium to selenium plus tellurium is about 1 to 1.l Referring toFigure-8, curves 22 24 and 26 illustrate the effect of substitutingincreasing amounts ofV tellurium and selenium.

Selenium, tellurium, zinc and cadmium may be introduced as elements oras compounds which are decomposedupon heating to, yield the elements. Itis preferred to introduce these elements as selenides and tellurides ofzinc and'cadmium. W l

The optimum amount of copper activator is approximately `0.01% by Weightwith respect tol the weight of the host crystal, that is, the combinedWeight ofzinc, cadmium, selenium and tellurium. The effect of varyingthe proportion of copper activator in the composition 0.95 ZnSe:0.05ZnTe:Cu (x) is shown in Table II.

Table II.--0.95 ZnSe:0.05 ZnTe:C|1(x) Relative peak Cu percent:emission: intensity 0.001 10 0.005 17 0.01 20 0.05 2.5

Silver may be substituted for copper as the activator to impart to thehost crystal similar luminescent properties. The proportion of activatormay be varied in between 0.0001 and `0.1% by weight with respect to theweight of the host crystal. Copper and silver preferably are introducedas salts such/as chlorides or nitrates.

AA flux is added to assist the recrystallization-of the host crystal.Chlorides, bromides and iodides of alkali metal, alkaline earth metaland volatile cations may be used. For example, calcium bromide andsodium iodide maybe usedi Ammonium: chloride is the preferred flux.Between 0.1 to 10.0 percent-by weight of iiux'with respect to the weightof host crystal may be used. The'preferred proportion is 2.0%.

Referring again to Figure 8, the effect of varying the firingtemperature is shown on curves 2'4,V 28, 30 and 32' for a phosphor ofthe composition 0.95 ZnSe:0.05

Table U13-n.95 znse.0.05 ZnTe:Cu (0.01)

' Relative peak Crystallization temperature: emission yintensityReferring to Figure 9, the effect of Varyingi the ,crystallizationtemperature upon the current density characteristic of the phosphor isshown Iby curves 34, 36, 38 and 40. v

Under oxidizing conditions during tiring, two phases are evident with a800 @crystallization tiring. A single phase appears at about 900 C. inan oxidizing atmosphere. However, this material exhibits a vdecreasedemission intensity under cathode ray excitation. A non-oxidizingatmosphere, such as argon, nitrogen or hydrogen, is preferred. Thepreferred atmosphere is nitrogen. The tiring may be carried out withinthe range between y650" C. and 1100 C., however, `a tiring temperatureof 900 C. is preferred. Firing should be carried on until the solidstate reaction take place. The duration of tiring depends in part on thebatch size. It is preferred to iire the batches of the examples forabout 30 minutes.

' `One vof the virtues of the phosphors of the invention, is that theyrexhibit exceedingly small color shift :ofthe emission when the phosphoris excited with varying densin ties of cathode rays. The results of thedemountable measurements of the color shift of a phosphor of theinvention compared with a Well-known copper-activated zinc selenidephosphor are given in Table IV. The values for the .vc-coordinate of theCIE chart are shown.

Table IV.C0lor shift Phosphor Defocused Focused Raster Raster ZnSe:Cu(0.01) O. 662 0.695 0.95 ZnSe:0.05 ZnTe: Cu (0.01) 0.662 0.662

III. SELENO-TELLURIDES FOR ELECTRIC FIELD EXCITATION Example 8.Mix 0.97mol pure zinc selenide, 0.03 mol pure zinc telluride, 0.15 weightpercent of copper as copper bromide and 10 weight percent of ammoniumbromide. The weight percents are with respect to the total weight ofzinc selenide plus zinc telluride. The mixture is then fired at about900 C. in an inert atmosphere such as nitrogen for about 30 minutes. Thefired material is cooled in nitrogen and then treated with an aqueoussolution of an alkali cyanide, such as sodium cyanide, to remove coppercompounds from the surface of the particles. The treated material isdried and is then ready for use as a red-emitting electroluminescentmaterial. 'Ihe composition of the fired product calculated from theinitial mixture of 0.97 ZnSe:0.03 SnTe: Cu (0.15):Br.

Referring to Figure l0, the spectral distribution of theelectroluminescence emission from this phosphor when excited in a 2 milgap with electric iields of the order of 250 volts per mil peak to peakat 10 kc. is shown by the curve 42. Curve 44 illustrates the spectraldistribution of a similar phosphor prepared Without tellurium excitedunder similar conditions. The substitution of tellurium for seleniumshifts the peak wavelength toward the red end of the spectrum andincreases the brightness of electroluminescence of the phosphor.

Example 9.-Slurry a mixture of 0.94 mol zinc selenide, 0.06 mol zinctelluride, 0.20 weight percent of copper as copper nitrate in tripledistilled water. Dry and re the mixture at about 950 C. in an atmosphereof hydrogen bromide for about 30 minutes. The composition of the firedproduct calculated Ifrom the initial mixture is 0.94 ZnSe:0.06 ZnTezCu(0.20):Br.

The electroluminescence brightness of the copperactivated zincseleno-telluride phosphors herein may be further increased through theuse of multiple activators. This may be accomplished by firstincorporating the copper activator and a igallium coactvator into thehost crystal material; and then incorporating the bromide. The followingexample illustrates this method.

Example 10.-Mix 0.97 mol zinc selenide, 0.03 mol zinc telluride, 0.15weight percent of copper, as copper nitrate, and 0.15 weight percent ofgallium as gallium nitrate. Then fire the raw batch at about 950 C. forabout 30 minutes in a nitrogen atmosphere. Upon cooling, mix 10 weightpercent of ammonium bromide with the fired product and relire at about950 C. for about 30 minutes in a nitrogen atmosphere. After refiring,the product is washed with a hot aqueous potassium cyanide solution andthen dried. The product exhibits a bright red electroluminescence andhas the following formulaV as calculated from the raw batch: 0.97ZnSe.0.03 ZnTezCu (0.l5):Ga(0.15):Br. p Table V includes a comparison ofthe brightness of this phosphor with other red-emittingelectroluminescent phosphors.

Between 0.05 and 0.25 weight percent of gallium may be used. Otherparameters may be varied as previously described. The proportion ofbromine and gallium is not critical because the proportion actuallyincorporated is limited by the proportion of copper incorporated in thehost crystal.

Table V Relative EL Emission Intensity (nt l0 kc.)

Phosphor Red Filter No Filter (wratten ZnSe: CusBr 0.030 0.95 ZnSe:0.05CdSe:Cu:Br 0. 20 0. O36 0.97 ZnSe:0.03 ZnTe:Cu:Br 1.4 0. 36 0.97ZnSe:0.03 ZnTezCuzBr: Ga 4. 6 2. 7

Selenium, tellurium and zinc may be introduced in elemental form or ascompounds which decompose upon heating to yield them into the reaction.It is preferred to introduce these ingredients as selenides andtellurides of zinc.

The ingredients of the raw batch should be of luminescence grade purity,and should contain no spectroscopically detectable impurities. Pure zincselenide may be obtained byprecipitation out of a pure aqueous zincacetate solution, using hydrogen selenide gas. Zinc telluride may beobtained by adding pure elemental tellurium in several small proportionsto molten zinc metal at about 800 C. in an atmosphere of hydrogen. Thetemperature is then raised to 1300 C. and held for l5 minutes to boiloff unreacted zinc and tellurium. After cooling, the zinc telluride isground and sifted.

Cadmium substituted for zinc, also shifts the peak wavelength of theproduct toward the red end of the spectrum. However, cadmium substitutedfor zinc decreases the electroluminescence emission intensity.

The substitution of tellurium for selenium in a zinc selenide hostcrystal is easily accomplished, producing red-emitting and infraredemitting electroluminescent materials with electroluminescence emissionintensities far greater than the corresponding cadmium containingmaterials. In addition, the red-emitting electroluminescent materialsherein,'are more color saturated than corresponding phosphors of thecopper-activated zinc-cadmium selenide system. Referring to the table,typical phosphors of each system are tabulated with their respectiverelative brightness.

It is preferred to substitute 0.1 to 10 mol percent of tellurium forselenium in the host crystal. The prelferred compositions herein are:

aZnSe:bZnTe:Cu(c) :Br where:

a=0.900 to 0.999 mols b=1.000-a mols c=0.5 to 0.25 weight percent withrespect to the weight of the host crystal.

Copper is introduced as a salt thereof such as copper chloride, copperbromide, copper nitrate, or copper oxide. The optimum amount of copperis approximately 0.5 weight percent with respect to the weight of hostcrystal; i.e. with respect to the combined weight of zinc, tellurium,and selenium. The proportion of copper may `be varied between `0.05 and0.25 weight percent with respect to the weight of the host crystal.

A bromide ux is added to the raw batch to assist the recrystallizationof the host crystal material during ring. Also, an activator proportionof the bromide is incorporated in the host crystal to improve theelectroluminescence brightness and color saturation ofthe product.Bromides of the alkali metals, alkaline earth metals and volatilecations may be used; for example, sodium bromide, ammonium bromide,calcium bromide and potassium bromide. Ammonium bromide is the preferredux. Between 1.0 andk 20 weight percent of the flux with respect to theweight of the host crystal may be used. The preferred'proportion is 10weight percent. In place of a flux, the raw batch may bev tired in anatmosphere containing a high vapor pressure of bromine, such as inA anatmosphere of hydrogen bromide.

The firing is preferably'carried out with a flux in an inert atmosphere,such as argon, nitrogen or hydrogen but preferably nitrogen.k The tiringmay tbe carried out within the range of 800 C. and 1050 C. The preferredtiring temperature is 900 C; Firing should be carried out until thesolid state reaction is complete. The duration of tiring time depends onthe batch size. It is preferred to iire the raw batch in 30 to 45minutes.

IV. SULFO-SELENO-TELLURIDES Sulfo-seleno-telluride phosphors hereinfollow the same teachings as inthe foregoing sections. Thus, startingwith any sulfo-selenide of zinc, cadmium or zinc-cadmium, tellurium maybe substituted for sulfur and/or selenium. The useful single phase solidsolutions are shown by the shaded area of Figure 11. Generally, wherethe sulfide is present in proportions mol percent or less of the hostcrystal, the telluride may be present in all proportions. Where thesulde is present greater than 5 mol percent, the telluride may bepresent in proportions up to 15 mol percent. n

Example 1].-Slurry 44.5 grams of zinc sulfide, 47.0 grams Zinc selenide,and 11.0 grams zinc telluride with 0.01 gram cupric chloride and 2 gramsammonium bromide in triple distilled water. Dry and fire the mixture at1000" C. in a nitrogen atmosphere for about 30 minutes. The compositionof the fired product as calculated from the metal mixture is 0.47ZnS:0.47 ZnSe:0.06 ZnTerCu (0.01).

Table VI lists further examples of the sulfo-seleno-tellurides. Allcathodoluminescence emission intensity readings (CL Int.) are normalizedagainst a Willemite Standard as 66. There is also shown the location ofthe peak cathodoluminescence (CL Peak) in A., the electroluminescenceemission intensity (EL Int.) and location of the peakelectroluminescence (EL Peak) in A. The numbered compositions arelocated on the triaxial diagram of Figure 1l.

Table VI Composition in Mol CL EL Percent Cu, Wt. No. Percent ZnS ZnSeZnTe Int. Peak 80 10 10 0. 1 21 5, 500 60 .80 10 0. 1 10 5, 700 130 6010 0. 1 1 5, 950 .10 80 10 0.1 0. 5 5, 950 75 20 05 0. 1 28 4, 900 475475 .05 0. 1 31 5, 500 20 75 05 0. 1 27 5, 600 55 30 l5 0. 1 10 5, 85035 .50 l5 0.1 0. 5 5, 950 90 10 0. 01 54 5,200 90 10 0. 01 9 6, 400 990l 0. 01 9 6, 100 0. 50 50 0. 0l 58 5, 800 1.00 0.01 20 6,400

1 Willemite Standard.

Referring to Figure 6, a cathode ray tube may include a luminescentscreen comprising a luminescent material of the invention. The cathoderay tube may comprise a tube base `69 including cathode ray gun 71 and aglass envelope comprising a neck portion 73, a conical portion 75 and aface plate 77. On the inner surface of the face plate 77 is disposed athin layer 79 of a composition including a vention suspended in adielectric medium, such as castor oil, between a pair of transparentelectrically-conducting electrodes. The phosphor emitsv light when avoltage is applied across the electrodes. Y Y

Referring to Figure 7, another electroluminescent cell comprises atransparent base 87 such as a sheet of glass, a transparentelectrically-conducting layer thereon, such as glass treated with tinchloride, a layer 85 thereon comprising a powdered phosphor of thisinvention dispersed in a solid or semi-solid dielectric medium ofreasonable light-transmitting properties such as wax, resin or plastics,and a metallic coating 81 thereon such as aluminum. The metallic coating81 and the transparent electrically-conducting coating 485 are connectedto a voltage source 93 through a switch 91 and a potentiometer 89. Uponapplying a Voltage, light may be observed through the transparent base87. Generally, the higher the electric eld across the electroluminescentlayer `83, the greater the emission intensity.

There have been described mixed chalcogenide phosphors, methods forpreparing such phosphors, cathode luminescent screens, and cathode raytubes including said phosphors, and electroluminescent screens anddevices including said phosphors. These phosphors and screens of theinvention emit blue to yellow radiation when excited. g

2. The phosphor of claim 1 wherein M1' M2 and M3 are each zinc.

3. A phosphor consisting essentially of a single phase solid solutionhaving the composition wherein: M1 is at least one member selected fromthe group consisting of zinc and cadmium, and M4 is one member selectedfrom the group consisting of copper and silver, x=0.999 to 0.001 mol,y=0.001 to 0.999 mol, x+y=l, and z==0.0 to 0.5 weight percent.

4. A phosphor having the composition wherein: x=0.999 to 0.001 mols,y=0.001 to 0.999 mols, x-|-y='1 and z=0.0 to 0.5 weight percent. y

5. A phosphor consisting essentially of 0.95 ZnSe:0.05 ZnTezCu (0.01).

6. A phosphor consisting essentially of 0.98 ZnSe:0.02 ZnTezCu (0.01).

7. An electroluminescent phosphor having a host cystal consistingessentially of a solid solution of zinc selenide,

0.1 to 10 mol percent of zinc telluride, and activator proportions ofcopper, and activator proportions of a member 11 of the group consistingof (1) bromine, and (2) bromine and gallium incorporated in said hostcrystal.

8. An electroluminescent phosphor having the molar compositionaZnSe:bZnTe:Cu(c) :Br where:

a=0.900 to 0.995 mols b=1.000-a mols, and

c==0.05 to 0.25 weight percent with respect to the weight of the hostcrystal.

9. An electroluminescent phosphor having the molar 10 compositionaZnSe.bZnTe:Cu(c) :Br:Ga Where:

a=0.900 to 0.995 mols b=1.000-a mols c=0.05 to 0.25 weight percent withrespect to the weight of host crystal. 15

References Cited in the tile of this patent UNITED STATES PATENTSLeverenz June 25, 1946 Leverenz .Tune 25, 1946 Leverenz July 26, 1949Leverenz Apr. 25, 1950 McKeag May 20, 1952 Kroger Dec. 30, 1952 PiperIan. 4, 1955 Larach Apr. 17, 1956 Nitsche Oct. 16, 1956 Crosby Dec. 31,1957 Mazo Aug. 12, 1958 UNITED STATES PATENT OFFICE CERTIFICATION OFCORRECTION Patent N0 2g978v417 April 4Q 1961 Simon Lerach It is herebycertified that error ppears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

' SEAL) Attest:

ERNEST W. SWIDER kttesting Officer DAVID L. LADD Commissioner of Patents

1. A PHOSPHOR HAVING THE MOLAR COMPOSITION
 3. A PHOSPHOR CONSISTINGESSENTIALLY OF A SINGLE PHASE SOLID SOLUTION HAVING THE COMPOSITION